Detection of Geomagnetic Signals as Precursors to Some Earthquakes in China

Round 1

Reviewer 1 Report

General comments

This paper presents a polarization analysis conducted using geomagnetic data based on five earthquake events that happened in China. The abstract is not well written as it did not provide a comprehensive overview (eg. focus, data used, conclusion) of the work. The introduction should also be improved in terms of motivation/justification of the current work. The discussion is lacking in terms of comparison of the current findings with the results of the previous studies. Furthermore, the Conclusion section should be separated from the discussion as the conclusion should summarize the main findings of the work.

 

Details comments

 

1. Line 40-42 : In order to prevent the phenomenon that the amplitude of horizontal component (H) is small when the geomagnetic activity is weak but the polarization value increases abnormally

Please revise this sentence. It is not clear what you want to do in order to prevent the situation/phenomenon.

 

2. Line 49: Nevertheless, we believe that this special phenomenon should be large-scale or even global, and it can be identified by multiple-station comparison

Please add reference here as this is the motivation of the current study.

 

3. What is the limit and criteria for a closest station to be chosen for this study? This is important to justify the selection of each station used for the particular earthquake.

Apart from that, why GLM station is not included in the analysis of Jinta earthquake, and why JYG station is not included in the study of Haixi earthquake?

  

4. Line 80: Wrong spelling for analysis.

 

5. Table 1: Please provide a full word for Dis and unit in the header of the last column table.

 

6. Figure 1 (a): Please include the location of the reference station CNH as well as CDP station for a better comparison. Please also provide latitude for the CNH station.

Figure 1(b): Please include the location of CNH station.

 

 

 

7. Please improve the way of writing the caption of Figure 2 to Figure 5.

 

8. Line 107-110: Some significant enhancements of YZH occurred a few days prior to the earthquake 107 and lasted for approximately 2 months afterward (Figure 2a). A similar increase in the YZG 108 plot is also observed (Figure 2b). The Dst index and a reference station (CNH observatory) 109 were selected for comparison, as shown in Figure 2c–2e.

The significant enhancements mentioned cannot be seen clearly in Figure 2. Authors need to provide a closure view by limiting the duration of the plots in order to confirm this statement. The authors also should mention the exact date or days when the first enhancements are obtained.

 

9. Figure 5: Please replace this figure with the actual Figure 5 as provided in the supplementary file.

 

10. Line 195-196: However, similar changes were not found for YZG, in contrast with the Jinta and Haixi earthquake results.

Please provide a plot to confirm this.

 

11. Line 224- 226: It is worth noting that in the results of previous studies, most of the electromagnetism anomalies ended before the earthquake occurred, while in this paper, the seismomagnetic anomalies continued until two months after the Jinta Ms 5.4 earthquake occurrence.

Please provide the reference and detailed discussion. Apart from that, the comparison of the same anomalies should be discussed. The term seismomagnetic is also not clearly discussed and should be introduced earlier in the Introduction part.

 

12. Line 235-237: What these abnormal earthquakes with precursor have in common? Their focal mechanism or seismogenic fault are some focus that needs to be studied next based on a large number of earthquake cases.

What do you mean by the abnormal earthquake here? Does it refers to the 5 earthquakes that showed the seismomagnetic anomalies in your study?

Author Response

As suggested by the reviewer, we have rewritten the Abstract, Discussion and Conclusions sections and all figures have been redrawn. The main revisions are as follows, more detailed revisions can be found in the manuscript:

 

• Line 40-42 : In order to prevent the phenomenon that the amplitude of horizontal component (H) is small when the geomagnetic activity is weak but the polarization value increases abnormally. Please revise this sentence. It is not clear what you want to do in order to prevent the situation/phenomenon.

   We have revised this sentence as ‘In order to prevent the phenomenon that the amplitude of horizontal component (H) is small when the geomagnetic activity is weak but the polarization value increases abnormally, Ida and Li et al. have eliminated the geomagnetic data of horizontal component with small amplitude during periods of weaker geomagnetic, and developed an improved polarization method.’

 

• Line 49: Nevertheless, we believe that this special phenomenon should be large-scale or even global, and it can be identified by multiple-station comparison. Please add reference here as this is the motivation of the current study.

We have added some references marked as[21-23] as reviewer’s suggestion.

 

• What is the limit and criteria for a closest station to be chosen for this study? This is important to justify the selection of each station used for the particular earthquake.Apart from that, why GLM station is not included in the analysis of Jinta earthquake, and why JYG station is not included in the study of Haixi earthquake?

   Based on the reviewer's suggestion, we have added an introduction to the rules for the selection of seismic events of line 91-95 in the text. We select earthquakes of magnitude greater than 5.0 in mainland China from 2008 to 2017, then calculated the epicenter distance from each earthquake to each geomagnetic station, and finally screened out the earthquake events which have the shortest distance from KSH/JYG/GLM as analysis objects. For example, we calculated the distance from the epicenter of the Jinta M5.4 earthquake to all geomagnetic stations. The closest distance to JYG station is 100 kilometers, and the distance to GLM station is 500 kilometers. Therefore, the data of JYG station was selected as the calculation object.

 

• Line 80: Wrong spelling for analysis.

    We have corrected the spelling.

 

• Table 1: Please provide a full word for Dis and unit in the header of the last column table.

    This is a mistake in the process of converting *.doc file to *.pdf file, and we have corrected them in progress.

 

• Figure 1 (a): Please include the location of the reference station CNH as well as CDP station for a better comparison. Please also provide latitude for the CNH station.Figure 1(b): Please include the location of CNH station.

   Based on the reviewer's suggestion, we have redrawn Figure 1 and added the location of the CDP and CNH station

• Please improve the way of writing the caption of Figure 2 to Figure 5.

    We have rewritten the caption of Figure 2 to Figure 5.

 

• Line 107-110: Some significant enhancements of YZH occurred a few days prior to the earthquake 107 and lasted for approximately 2 months afterward (Figure 2a). A similar increase in the YZG 108 plot is also observed (Figure 2b). The Dst index and a reference station (CNH observatory) 109 were selected for comparison, as shown in Figure 2c–The significant enhancements mentioned cannot be seen clearly in Figure 2. Authors need to provide a closure view by limiting the duration of the plots in order to confirm this statement. The authors also should mention the exact date or days when the first enhancements are obtained.

  Based on the reviewer's suggestion, we have added descriptions of anomaly start and end times and anomaly magnitudes in each earthquake case study.

 

• Figure 5: Please replace this figure with the actual Figure 5 as provided in the supplementary file.

We have replaced this figure with the actual Figure 5 as provided in the supplementary file.

 

• Line195-196: However, similar changes were not found for YZG, in contrast with the Jinta and Haixi earthquake results. Please provide a plot to confirm this.

Based on the reviewer's suggestion, we have redrawn Figure 5 and added the plot of Y_ZG.

 

• Line 224- 226: It is worth noting that in the results of previous studies, most of the electromagnetism anomalies ended before the earthquake occurred, while in this paper, the seismomagnetic anomalies continued until two months after the Jinta Ms 5.4 earthquake occurrence.Please provide the reference and detailed discussion. Apart from that, the comparison of the same anomalies should be discussed. The term seismomagnetic is also not clearly discussed and should be introduced earlier in the Introduction part.

    We have introduced ‘seismomagnetic’ in the Introduction part and added a detailed comparison with the results of previous studies in the conclusion section (Line 305-324).

 

 

• Line 235-237: What these abnormal earthquakes with precursor have in common? Their focal mechanism or seismogenic fault are some focus that needs to be studied next based on a large number of earthquake cases.What do you mean by the abnormal earthquake here? Does it refers to the 5 earthquakes that showed the seismomagnetic anomalies in your study?

  Based on the reviewer's suggestion, we have added some comparisons and statistics about earthquakes with seismomagnetic signals and earthquakes without seismomagnetic signals in ‘Discussion’ (Line 254-280).

Author Response File: Author Response.docx

Reviewer 2 Report

This paper reported the geomagnetic precursor prior to some earthquakes in China. The manuscript needs some revision before it is accepted and published. Below are some suggestions and comments.

 

1. Figure 1

Please put the global map of China or the world map so that the reader can understand the detailed location of your study.

2. Equation (2).

Eq. (2) presents that the G component is composed of H and D components. Hayakawa (12, 21) did not mention it. Please read their papers carefully. The D component is the declination, and its unit is in degree. The unit of H and Z components is Tesla. I think it is better to use the G components as the square root of the X and Y components since the units of X and Y components are also Tesla.

3. I think it is better to put all 37 earthquakes which you analyzed in your study so that you can comprehensively discuss why the precursor only appears prior to 4 earthquakes. What is the most influential in generating the precursor? The distance between EQ epicenter and station location? The magnitude of the earthquakes?   

Comments for author File: Comments.pdf

Author Response

As suggested by the reviewer, we have rewritten the Abstract, Discussion and Conclusions sections and all figures have been redrawn. The main revisions are as follows, more detailed revisions can be found in the manuscript:

 

• Figure 1Please put the global map of China or the world map so that the reader can understand the detailed location of your study.

   Based on the reviewer's suggestion, we have redrawn Figure 1 and added the location of the CDP and CNH station.

 

• Equation (2). (2) presents that the G component is composed of H and D components. Hayakawa (12, 21) did not mention it. Please read their papers carefully. The D component is the declination, and its unit is in degree. The unit of H and Z components is Tesla. I think it is better to use the G components as the square root of the X and Y components since the units of X and Y components are also Tesla.

Based on the reviewer’s suggestion, we have added some references to formula (2). In addition, it needs to be explained that in China's 1s sampling geomagnetic observation, the unit of declination D has been converted from angle to Tesla, so it is the same unit system as H and Z. In addition, DHZ are the observation components under the geographic coordinate system, which actually represents the XYZ under the geomagnetic coordinate system.

 

• I think it is better to put all 37 earthquakes which you analyzed in your study so that you can comprehensively discuss why the precursor only appears prior to 4 earthquakes. What is the most influential in generating the precursor? The distance between EQ epicenter and station location? The magnitude of the earthquakes?   

Based on the reviewer’s suggestion, we have put all 37 earthquakes in our study and discussed some possible rules or reasons why the precursor only appears prior to 4 earthquake. As showed in Line254-280 of ‘Discussion’ .

Author Response File: Author Response.docx

Reviewer 3 Report

The authors presented the use of geomagnetic field data obtained from three stations to observer pre-seismic anomalies prior to five earthquakes in China. The ULF polarization ratio analysis was shown to be effective to reveal anomalies prior to the earthquakes in certain frequency ranges according to skin depth theory. 

The reviewer thinks that the addition of such studies is always welcome in strengthening the validity of 'seismo-electromagnetic' signals as an alternative to the conventional seismic-based methods. However, considering that the method used in this study has been implemented for quite a while by many past studies, the findings and theoretical discussions in this paper left much to be desired as no notable results were presented. The earthquakes that were studied are somewhat old. The reviewer suggests that the authors enrich the discussions in place of the unremarkable results. 

Specific comments are stated in the attached file.

 

Comments for author File: Comments.pdf

Author Response

As suggested by the reviewer, we have rewritten the Abstract, Discussion and Conclusions sections and all figures have been redrawn. The main revisions are as follows, more detailed revisions can be found in the manuscript:

 

• When a source is cited in the middle of a sentence, the author's name and the year of the citation are usually stated. Please check with MDPI format about this. The same concern applies for all other citations like this one.

Based on the reviewer's suggestion, the citation format of all references in the full text has been revised.

 

• Please cite your source. Also, is 'm' (meter) the unit for resistivity?

   Based on the reviewer's suggestion, we have added the reference for Equation 2, and we have determined that the unit of resistivity in the formula is meters.

 

• No prior information was given about this station. It is better to include the information about all reference stations in Table 1 and Figure 1.

As suggested by reviewer, we have added some information about reference station which were displayed in Figure 1, and we have gave an explanation of why it was chosen as a reference table. We have checked the quality monitoring reports of the China Geomagnetic Network Center in the past five years. The 1s sampling stations with better data quality are KSH, LIJ and CNH stations. The observation data of LIJ station only started in 2017, so we have selected CNH as reference stations.

 

• A magnetometer located at higher latitude would measure a greater vertical component and weaker horizontal, not the other way around. Please check this.

  Based on the geomagnetic observation data in mainland China, we have analyzed the variation of the DHZ component spectral amplitude with the geomagnetic latitude, and the specific results are shown in the figure. It is obvious that the horizontal components D and H both show a trend of increasing with the increase of latitude, while the vertical component Z is not significant. Related research results have been published as follows: Yao, X. Y.; Yang, D. M.; Chen, H. R., He, Y. F.; Gao, D. P. Analysis on temporal-spatial distribution of the short-period geomagnetic activities. Chinese J. Geophys, 2012, 55(8), 2660-2668.

 

 

• Why does this figure show an earthquake of M5.0? Aren't the earthquakes for this case study M6.7 and M7.4 only? Also, please label all three earthquakes in this figure.

  Due to the author's negligence, the wrong picture has been placed, and the picture has been corrected.

 

• Most of the references are quite old. Only 3 references are within 5 years (2016 - 2021). It gives an impression that this present study is outdated. Please consider adding/replacing the references with more recent ones.

  As suggested by the reviewer, we have added recent references on corresponding researches and a comparative discussion of these researches have been carried on in the discussion section in our paper.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The revised manuscript has covered most of the issues raised in the previous review. However, some parts still need to be clarified/revised as follow;

 

1. The caption figures need to be revised. Avoid repetition of words in mentioning panels of (a), (b), etc.. For example, Figure 6. Scatter diagrams of magnitude and epicentral distance for all (a) 37 and (b) 30 earthquakes.
2. Provide a reference for line 410.
3. The conclusion should be simplified and answer the objectives of this work. Comparision and discussion with the previous study should be moved to the Discussion section.

 

Author Response

The manuscript has been revised as reviewer's comments as follows, more detailed revisions can be found in the manuscript through the ’Track Changes’ function.

1. The caption figures need to be revised. Avoid repetition of words in mentioning panels of (a), (b), etc.. For example, Figure 6. Scatter diagrams of magnitude and epicentral distance for all (a) 37 and (b) 30 earthquakes.

 Based on the reviewer's suggestion, we have revised all figure captions in the manuscript .

2. Provide a reference for line 410.

We have provided some references for this sentence.

3. The conclusion should be simplified and answer the objectives of this work. Comparision and discussion with the previous study should be moved to the Discussion section.

   Based on the reviewer's suggestion, we have moved the comparison and discussion with previous study to the Discussion section

Reviewer 2 Report

Dear author,

Thank you very much for your revision. I think the revised manuscript is much better to explain the phenomena of the earthquake precursor in China. There is a little improvement by the author before the manuscript is accepted.

1. I think it is better to move the second paragraph of the Conclusion to the Discussion since it is not the conclusion of your study.
2. It is also some typos in the Conclusion section, for example: [xxxx], Thier study, and so on. Please check your manuscript carefully. 

Author Response

The manuscript has been revised as reviewer's comments as follows, more detailed revisions can be found in the manuscript through the ’Track Changes’ function.

1. I think it is better to move the second paragraph of the Conclusion to the Discussion since it is not the conclusion of your study.

   Based on the reviewer's suggestion, we have moved the comparison and discussion with previous study to the Discussion section

2. It is also some typos in the Conclusion section, for example: [xxxx], Thier study, and so on. Please check your manuscript carefully. 

  We have revised this typo and checked manuscript.

Reviewer 3 Report

1. Line 78: "Nevertheless, we believe that this special phenomenon should be large-scale or even global [21-23], .."
   I still don't think this sentence is appropriate as the authors already provided the studies that did that but still used the word "believe" as if it is just a potential. Use the word "it was shown" or "it was demonstrated" etc.
2. There should be a whitespace between an in-text citation with the word in front of it, e.g., "..or even global [21-23]".
   
   
3. All figure captions need to be repaired in terms of their format and brevity. The arrangement of the caption is still incorrect; please refer to any other papers as I think the typical/standard style of writing captions is being used by almost everyone.
4. What is [xxxx] in Line 410. The manuscript submitted for review should be complete.
   
   
5. I suggest the manuscript to be sent for English proofreading.

Author Response

The manuscript has been revised as reviewer's comments as follows, more detailed revisions can be found in the manuscript through the ’Track Changes’ function.

1. Line 78: "Nevertheless, we believe that this special phenomenon should be large-scale or even global [21-23], .."I still don't think this sentence is appropriate as the authors already provided the studies that did that but still used the word "believe" as if it is just a potential. Use the word "it was shown" or "it was demonstrated" etc.

   Base on reviewer’s suggestion, we have revised this sentence as ‘Nevertheless, it was demonstrated that this special phenomenon should be large-scale or even global[21-23], and it can be identified by multiple-station comparison’

2. There should be a whitespace between an in-text citation with the word in front of it, e.g., "..or even global [21-23]".

 We have checked this manuscript and revised all citation type.

3. All figure captions need to be repaired in terms of their format and brevity. The arrangement of the caption is still incorrect; please refer to any other papers as I think the typical/standard style of writing captions is being used by almost everyone.

    We have revised all figure captions in the manuscript.

4. What is [xxxx] in Line 410. The manuscript submitted for review should be complete.

We have provided some references for this sentence.